There are a number of factors which affect the ability of a farmer to produce high quality, high yield crops. Such factors include environmental conditions, land, and the types and the amounts of fertilizer used. Other factors which add considerably to the expense of raising crops include the type and amount of labor and machinery available to the farmer. Although all these factors have considerable influence on the quality and quantity of the yield, perhaps none of them is as important as the starting seeds. Accordingly, considerable efforts have been made to produce high quality inbred and hybrid seeds which produce high quality and high yield crops.
Advanced breeding techniques have made it possible to improve a number of characteristics of the resulting crops including characteristics such as crop quality, yield, disease and drought resistance. However, breeding techniques have limitations and require substantial periods of time in order to develop seeds which result in crops having all of the desirable characteristics for a particular area. Further, such breeding techniques often result in improving one characteristic to the detriment of another equally important characteristic.
When breeding seeds to produce crops in a temperate region such as the United States, the breeder must be conscious of factors such as changing temperatures, moisture and the photoperiod or amount of light available during the growing season. Seeds and cultivation practices are chosen in order to take the maximum advantage of each of the environmental conditions which the crops will be exposed to. Early planting of relatively short season varieties has become an important part of current agricultural practice.
Timing of the planting operation is frequently compromised by local weather conditions, equipment, and labor availability. Fields planted earliest in the spring will have a longer growing season but will be subjected to greater risk due to weather conditions and disease. Seeds planted later in the season are likely to provide lower yields due to a shorter growing period but are subjected to less risk. One of the most critical periods for crops is the period between the initial planting of the seed and germination. The significance of this period is explained further below.
In order for the seed to begin germinating it first must take in water; a process referred to as imbibition. Unless imbibition takes place, germination will not occur. Conversely, once imbibition begins, germination must occur within a relatively short period of time or the seed may become diseased and/or die. Accordingly, it would be desirable to have seeds which could be planted in the fall or early spring, which seeds would delay imbibition until the critical soil temperature range most favorable for germination is reached. Most seeds, however, will begin imbibition when water is present irrespective of the temperature of the soil. If the seed takes in sufficient amounts of water and the temperature remains cool, germination will be slow or will not occur and the seed will be more vulnerable to attack by diseases such as fungus.
U.S. Pat. No. 3,545,129 issued Dec. 8, 1970 to Schreiber et al. discloses a multiple coated seed. The seed includes an inner coating which is slowly permeable to water, an intermediate coating which is also semi-permeable to water, and an outer coating which is substantially impermeable to moisture but is fissionable at a frost temperature. The object of the invention is to treat seeds with these multiple coatings so that the seeds may be planted in the fall and the advantages of early emergence in the spring can be obtained.
In U.S. Pat. No. 3,698,133 issued Oct. 17, 1972 to Schreiber, another multicoated seed is disclosed. The coated seed includes an inner porous coating which is permeable to water and an outer coating having controlled water permeability so as to control the water imbibition of the seed to the extent necessary to delay germination until environmental conditions are satisfactory for crop growth.
A somewhat different approach to providing coated seeds is disclosed within U.S. Pat. No. 4,779,376 issued Oct. 25, 1988 to Redenbaugh. In accordance with this disclosure, the seeds are combined with beneficial adjuvants and encapsulated in a saturated hydrogel matrix. The system provides specific adjuvants to the seeds in order to improve their growth.
It has been demonstrated that imbibitional chilling injury to cotton and soy beans can be reduced by coating such seeds with lanolin. Work carried out in this area is disclosed within D.A. Priestley and A.C. Leopold, "Alleviation of Imbibitional Chilling Injury by Use of Lanolin" Crop Science 26, 1252 (1986).
Each of the systems mentioned above have certain advantages and practicalities in that the coating of seeds does not add substantial expense as compared with other agricultural expenses such as the cost of land, machinery and labor. Although these systems can provide advantages, none of the systems optimize the concept of delaying germination by using a coating which changes permeability (and thus affects imbibition) based on temperature so as to result in a coated seed which begins imbibition and thus germination under the most favorable environmental conditions. Accordingly, there remains a need for a coated seed which obtains the advantages of delayed germination in a manner which is both temperature and moisture dependent. The present invention provides such a coated seed.